Struck: A Japanese heavy cruiser lies low in the water after being bombed by US naval aircraft during the Battle of the Midway.AP

On June 4, 1942, a battle off Midway Island marked the dawn of the United States Navy as the most powerful sea force in the world. Seventy years later, a civilian “battle” may doom its reach and power for good.

Then the enemy was imperial Japan. Today, it’s the administration and Congress, who seem unable or unwilling to stop defense cuts that will leave America vulnerable and the world more dangerous. We’re fast approaching the point where the US Navy can no longer guarantee the safety of the world’s sea lanes, on which our economic future depends.

Seventy years ago, shorn of its battleships by the attack on Pearl Harbor, the Navy found itself on the defensive everywhere in the Pacific. And an overwhelming Japanese task force hoped to trap three of our fleet’s five surviving carriers — Hornet, Enterprise and Yorktown — off Midway and wipe out America as a naval competitor.

But a US observation plane spotted the Japanese first. Flying out with incredible courage against a foe who enjoyed superior planes and numbers, Navy torpedo planes and dive bombers caught four Japanese carriers (Soryu, Akagi Kaga and Hiryu) preparing to attack the Marine airfield on Midway — and sent them to the bottom, along with a quarter of Japan’s most experienced air crews.

With just two large fleet carriers left, the Japanese navy was no longer capable of dominating the seas.

In one momentous afternoon the Navy not only avenged Pearl but also reversed the tide of war in the Pacific. Later victories in the battle of the Philippine Sea and Leyte Gulf (and the landings on Tarawa, Guam, Iwo Jima and Okinawa) were all made possible by the decisive win at Midway — and by a Navy that would grow from a crippled giant (211 surface vessels) on Dec 8, 1941, to more than 6,768 active vessels, including 833 surface warships and 232 submarines: the most powerful force afloat for the next six decades.

Now fast-forward to 2012.

President Obama took office with a Navy reduced from a Reagan-era peak of 594 active ships in 1987 to 285 in 2009 — a US fleet smaller than before World War I.

Most naval experts agree we need a minimum of 320 to 350 ships — barely one for every 400,000 square miles of ocean — to police the sea lanes on which international trade depends and to protect our strategic interests. But Obama wants to retire another 11 ships.

Worse, if budget sequestration starts to kick in this January — and the president and Democrat-controlled Senate are doing nothing to stop it — the Navy may have to shrink by another 60 ships and subs, with two full carrier battle groups going into retirement. Chief of Naval Operations Jonathan Greenert has testified the cuts would inflict “irreversible damage” on the once-proud US Navy.

Pacifists might cheer that news. But the purpose of a strong fleet isn’t to fight wars but to prevent them by defusing potential crises, policing global hot spots and deterring would-be aggressors with a forceful US presence at sea and (thanks to our carriers) in the air.

In 1998, we had on average 60 ships under seaway on any given day. Today, it’s just 20. For missions from dealing with pirates on the Somali coast to monitoring North Korea’s missile launches to keeping Iran from making good on its threats to close the Straits of Hormuz, we increasingly have to call in other nations’ navies to help.

What happens if a crisis blows up with a country like China or Russia and those other nations decline to help?

The Japanese attacked Pearl Harbor not because they saw our Navy as strong but because they saw it as weak — vulnerable to a single devastating attack. Midway proved them wrong. A combination of Navy and Marine courage and resourcefulness, brilliant code breaking and sheer luck overcame tremendous odds.

Japan lost four carriers, a cruiser, 248 planes and 3,000 dead. But our losses were sobering: one carrier, Yorktown, and one destroyer lost, plus 150 aircraft and 305 lives.

Seventy years on, let’s not ask our sailors and naval aviators to fight from a position of weakness again.